Hidroacanthoma simplex is a benign tumor of the skin, macroscopically resembling seborrheic keratosis or Bowen's disease and histologically mimicking clonal-type seborrheic keratosis. We observed a plaque of 70 × 50 mm on the right flank part. From clinical appearance, we suspected Bowen's disease; however, based on immunohistochemical findings, we made a diagnosis of hidroacanthoma simplex.
Keywords: Immunohistochemistry; Lumican staining; Seborrheic keratosis.